As one method for synthesizing liquid fuels from a natural gas, a GTL (Gas To Liquids: liquid fuel synthesis) technique of reforming natural gas to produce a synthesis gas containing a carbon monoxide gas (CO) and a hydrogen gas (H2) as the main components, synthesizing hydrocarbons with this synthesis gas as a source gas by the Fischer-Tropsch synthesis reaction (hereinafter, in some cases, referred to as an “FT synthesis reaction”), and further hydrogenating and fractionating the hydrocarbons to produce liquid fuel products, such as naphtha (raw gasoline), kerosene, gas oil, and wax, has recently been developed.
The liquid fuel products produced by using hydrocarbon compounds obtained by a FT synthesis reaction as a feedstock contain a large amount of paraffins and hardly any sulfur content. Therefore, as shown in Patent Document 1, such liquid fuel products have been paid attention to as environmentally-friendly fuels.
When the hydrocarbon compounds obtained by the FT synthesis reaction is fractionally distilled in a fractionator, a naphtha fraction having small numbers of carbon atoms is drawn from the upper part of the fractionator. Since such a naphtha fraction contains a large amount of olefins as well as alcohols, as shown in Patent Document 2, it is necessary to subject the naphtha fraction to a hydrotreating to produce saturated compounds.